In the prior art, rocket engine combustion chambers are manufactured by electroforming of nickel or the like. For rocket engine combustion chambers having a larger diameter, it is often practiced to apply a ceramic layer of zirconia, yttria or ceria, by spraying, to the inner surface of an electroformed nickel combustion chamber in order to increase strength and heat resistance. In operation, the rocket engine combustion chamber wall is cooled with the rocket propellant as a coolant (complete regenerative cooling) in order to protect the wall from propellant combustion gases at temperatures of from about 2,000.degree. to 3,000.degree. K. For increased cooling efficiency, cooling is done such that the coolant may not boil.
The combustion chambers formed from a metal such as nickel, however, suffer from several problems that not only an improvement in heat resistance of the combustion chamber is needed to accommodate the increased thermal flux from the combustion chamber inner surface due to increased heat transfer, but the wall thickness of the combustion chamber must be increased to alleviate thermal loads, both resulting in an increased size of cooling mechanism which is disadvantageous for weight reduction of the combustion/propulsion mechanism.
The ceramic layer sprayed to the inner surface of the combustion chamber has a durability problem associated with essentially poor adhesion between the ceramic layer and the combustion chamber-forming metal, typically nickel. A rapid temperature rise of the combustion chamber inner surface at the start of combustion of rocket propellant most frequently causes the sprayed ceramic layer to spall, eventually peeling off or cracking. Then the sprayed ceramic layer fails before fully exerting its thermal insulation and wear resistance against combustion gases exiting at a super high velocity.
For rocket engine combustion chambers having a smaller diameter, on the other hand, it is difficult to spray ceramic material to the inner surface of the combustion chamber. For the purpose of protecting the combustion chamber wall during combustion, the combustion chamber on the outer surface is cooled with the propellant as a coolant, and at the same time, part of the propellant is injected along the inner surface of the combustion chamber (partial regenerative cooling). This results in an increased loss of energy.